With the development and the popularization of wearable devices, instruction set of wearable devices is booming, and the number of instruction is also increasing remarkably. However, as the application function of wearable devices increases, the duration capability of solar cell does not keep pace with the diversification and complication of application. Therefore, a solar cell for the wearable devices with elevated duration capability is demanded urgently. One of the critical factors for duration capability of solar cell is the stability of cathode of a solar cell unit (also called solar unit in the following passages).
Therefore, it is desired to provide a cathode of solar unit with high stability.